1. Field of the Invention
The present invention relates generally to communications systems, and more particularly to an architecture for transforming a software defined radio having independently operated channels into a fully shared multi-channel software defined radio.
2. Description of Related Art
A coherent digital communications system typically requires that signal phase, symbol and frame synchronization be performed at the system receiver, as the phase of the transmitted carrier signal must be accurately reproduced at the receiver. In addition, the receiver must have the capability of determining the timing boundaries of the transmitted symbols. This capability is referred to as symbol synchronization.
In wireless digital radios having multi-element antenna arrays, multi-path fading often significantly degrades communications system performance. The effects of fading can be countered through spatial diversity techniques in which antenna elements are separated as a function of signal wavelength so that associated Rayleigh fading is independent at each antenna. Consequently, when a deep Rayleigh fade occurs at one of the antennas, other antennas in the array will likely have corresponding stronger signal reception.
Current spatial diversity techniques attempt to overcome the effects of signal fading by estimating frequency offset and carrier phases and attempt to determine symbol timing. However, these techniques typically add a significant amount of complexity to the radios. In addition, in a radio such as a software defined radio in which digital signals are communicated over wireless channels, a symbol synchronization technique must be robust enough so that the bit error rate (BER) performance of the received data is not degraded. The robustness of the synchronization technique is important, as such systems are often utilized in hostile environments in which interferers and jammers weaken the capability of the radio to synchronize with the desired signal, and in which frequency-hopped signals require the radio to resynchronize after each hop. Because current spatial diversity techniques assume signal synchronization, the techniques therefore often do not provide a symbol synchronization technique that is robust enough for problematic channel operating conditions such as those described above.